ProFont.
It is the best programming font I have seen and I use it all the time (for most stuff - not just programming), both on Windows and Mac - even though it looks slightly better on Mac. Do **not** antialias it and use 9 pt (else it looks awful). Before I switched to ProFont I had to use at least 12 pt (Monaco for Mac and Consolas on Win) - I am getting old I guess - but ProFont is very readable at only 9 pt.
Here is a screenshot so you can get the feel of it. For example, see how it clearly distinguishes between "0" (number zero) and "O" (capital letter O) and between "1" (number one), "l" (lowercase letter L) and "I" (capital letter I) - something many fonts (including Monaco) have a problem with. But you should really try it out yourself.
